Steel rule dies are commonly used for cutting cloth and cloth-like material such as natural textiles, and synthetic material such as vinyl. Steel rule dies are particularly advantageous in the repetitive cutting of specific shapes such as apparel, automobile upholstery and trim panels, and the like. In brief, a steel rule die typically comprises a base or backing board in which a slot or groove matching the pattern to be cut is sawn, and a length of steel rule embedded in the board with the sharpened exposed upper edge extending therefrom. The die is used in combination with a cutting pad and a press which may either be single-cut, progressive or increment feed.
A problem arises when it is necessary or desirable to cut relatively thick but compressible materials such as foamed-backed materials, foam rubber, waddings, battings, paddings, high pile materials, and other fluffy or spongy materials. A stack or a particularly thick single layer of such materials is sufficiently unstable that an accurate cut is often not possible using conventional techniques.
One approach to the more accurate cutting of compressible materials is disclosed in U.S. Pats. Nos. 3,790,154; 3,765,289; and 3,815,221, all assigned to Gerber Garment Technology, Inc. of Hartford, Conn. These patents, and other related patents assigned to Gerber, disclose a vacuum table which is used primarily to hold sheet material in place while it is cut by a two-axis single blade jigsaw type cutter. According to these patents, a sheet of mylar or oher air-impervious material can be placed over a stacked of compressible materials such that the vacuum table creates a vacuum under the sheet to pull downwardly on the sheet and maintain the entire stack in a stable, compressed condition during the cutting process. In a further Gerber U.S. Pat. No. 4,060,016, the jigsaw type cutter is replaced with a rotatable turret carrying a plurality of blanking dies which are selectively rotated into position and driven downwardly through the air-impervious sheet and through the stacked materials to form a stack of cut patterns corresponding to the shape of the particular blanking die selected.
In all of the patented systems, the board on which the stacked material is located must be capable of receiving the penetrations of the reciprocating knife, or the downward thrust of the blanking dies, as well as maintaining a vacuum for the principal purpose of holding the stack in place and for the secondary purpose of evacuating the volume under the air-impervious sheet.
All of these patented arrangements also suffer from the disadvantage that the air-impervious sheet is cut in the process of cutting the stacked material layers with a consequent loss of vacuum and thereby a loss of stability of the stack. And whereas certain of the Gerber patents describe means for "healing" the cut in the air-impervious sheet behind the cutting member, these healing arrangements unduly complicate the overall cutting apparatus and/or are not totally successful in preventing loss of vacuum with a consequent loss of stability of the stack.
It has been proposed to use stationary steel rule blanking or cutting dies with air-evacuation compression so as to facilitate and improve the use of such dies to cut compressible materials. These proposals have involved the use of an air-impervious cover means over a stack of compressible material positioned on the steel rule upper edge to define a vacuum chamber and means for evacuating the vacuum chamber to compress and reduce the thickness of the stack of layers before cutting the layers with the rule.
It has further been proposed to support the base of the steel rule die on a die plate or die carrier and to provide a frame which surrounds the steel rule die and includes means which are operative to exhaust air from the vacuum chamber formed beneath the airimpervious cover to compress and reduce the thickness of the stacked materials prior to the cutting operation. This arrangement allows a single die plate or carrier to be used with a plurality in interchangeable steel rule dies so as to obviate the need for providing a vacuum device as a part of each steel rule die. Whereas this arrangement is cost-effective and efficient, it has the disadvantage of requiring the extremely heavy steel rule dies to be lifted into and out of their positions within the frame of the die plate or carrier. This heavy and cumbersome lifting operations slows the overall cutting process considerably and, in extreme cases, requires the use of special lifting equipment.